"Disconnected" usually means that accounts, permissions, or network connections have changed. When a service reports a "Disconnected" status, the real explanation of the problem is detailed in the corresponding log file.

It would be nice if we could take a peek in those three QlikView service log files...

Hmmm. Could be a DNS issue. Have you tried substituting IP address instead of servername in the URLs for each of the disconnected services? So, for example, for DSC, in QMC, navigate to System > Setup > Directory Service Connectors > DSC@ > General tab > URL.

However, the DSC log tells a good story. Apparently there appears to be a problem when trying to reach the domain controller (or LDAP server if that's what your client is using) If accounts are defined on server LDAP://bunzl.internal and that one cannot be reached, in an AD landscape all sorts of things start going wrong...

Typically when I have run into this error, communication between QVS and the Root Folder/Mounted Folders has been interrupted. I believe this lends credence to your original suspicion of a DNS issue.

So everything was working fine yesterday and then all of a sudden the services are showing as disconnected? As Peter mentioned previously, the "Disconnected" error typically refers to accounts/permissions or network issues. How are the different QV services authenticated - via Windows security groups or certificates? If Windows security groups would check for password changes or permissions. If certificates, ensure that the certificate hasn't expired. If all of these are good, then investigate potential network issues. Would start with DNS as I previously mentioned.

Updated the Lef Details – just to be sure as they were showing end date of 2017-09-29

Change the Service logon user to a different domain user with the correct permissions – and restarted the services

Delete the user name and password help against LDAP against the Active Directory option, this isn’t required when the service user is a domain user and appeared to have an incorrect password.

Everything is now up and running

The issue appears to be a corrupted profile on the service user account, would recommend that you create a new Domain user to run the services as a member of local administrators and Qlikview Administrators